Brian O’Sullivan ’75 passed away unexpectedly on March 8. Brian was born in Queens, New York, and grew up in Granby, Massachusetts. At Dartmouth he majored in biology and led the Dartmouth Film Society. Two years after graduating, Brian attended Dartmouth Medical School. After a distinguished career at the University of Massachusetts Medical School, he returned to Hanover to join the Children’s Hospital at Dartmouth-Hitchcock Medical Center in 2014. Brian enjoyed a reputation as a remarkable academic physician and educator whose work and scholarship improved the lives of children with cystic fibrosis and other respiratory disorders. In 2020 Brian became codirector of the N.H. Cystic Fibrosis Center at Dartmouth and in September 2025 stepped into the interim role of vice chair for research in the department of pediatrics. During his career, Brian earned national recognition for scholarship and leadership in cystic fibrosis research. His work appeared in leading journals—including The New England Journal of Medicine, The Lancet, and the Journal of the American Medical Association—helped shape national guidelines for cystic fibrosis care, and was supported through numerous National Institutes of Health- and Cystic Fibrosis Foundation-funded studies. He is survived by his wife, Susan; and children Conor and Whitney.